The present invention relates to a prosthetic implant and to a surgical tool for gripping the prosthetic implant during a surgical procedure.
The replacement of all or a part of the bone surface of an articulation with a prosthetic implant has become a common surgical procedure. The procedure requires the surgeon to exercise both precision and delicacy in the placement of the prosthetic implant. However, it is frequently necessary for the surgeon also to exercise a degree of force, sometimes a vigorous force, in order to situate the prosthetic implant in a desired location on the bone surface.
For example, in an operation to insert a prosthetic acetabulum in a patient""s pelvis the surgeon first uses a reamer to grind a cavity of appropriate size in the patient""s pelvis. The surgeon then inserts an acetabular cup into the cavity. By xe2x80x9cappropriate sizexe2x80x9d is meant a size which is selected by the surgeon as being the most appropriate for that particular patient. Normally, it is desirable to retain as much of the original healthy bone surface as possible.
Commercially available acetabular cups are sold in a range of sizes to suit the needs of individual patients. Generally, acetabular cups are available in sizes of from 42 mm to 62 mm diameter, with 2 mm increments between neighbouring sizes.
Prosthetic acetabular cups generally require the use of an insertion tool to achieve correct positioning of the prosthesis in the patient""s pelvic cavity. A typical insertion tool is described in U.S. Pat. No. 4,305,394 (Bertuck).
There are a number of different types of prosthetic acetabular cups. Firstly, cups made from polyethylene are available. Polyethylene cups are cemented into the acetabulum and require only light pressure to seat them in the cement. Secondly, there are cups which comprise a metal shell for insertion into the pelvic cavity and a polyethylene liner for articulation with the femur. Some polyethylene cups with metal shells are implanted without cement and rely on a jam fit between the metal shell and the patient""s acetabulum. Often these metal shells have surfaces or coatings which encourage bone to grow into them over time. A typical coating material is hydroxyapatite. With this type of prosthesis, the polyethylene liner is snapped or screwed into the metal shell after the metal shell has been seated in the acetabulum to form the socket part of the patient""s joint.
Cups which rely on a jam fit require a greater force to be applied via the insertion tool than is the case with cemented polyethylene cups. This force is usually applied as a direct impact into the acetabulum, for example by use of a mallet on the free end of the insertion tool. However, it may also be necessary to adjust the angular position of the cup in the bone or to take it out if positioned incorrectly. Therefore the insertion tool must positively grip the cup by some mechanical feature. This feature cannot impinge upon the outside of the metal shell because the insertion tool may then become trapped between the shell and the bone. Also there is little room around the rim of the shell because the wall thickness of the shell is generally kept to a minimum. Therefore the insertion tool usually grips on a mechanical feature on the inner hemisphere of the metal shell. An insertion tool of this type is described in International Patent Publication No. WO 94/21199 (Howmedica Limited). The mechanical feature is usually designed so as to cause minimum compromise to the function of the prosthetic hip joint. As a result it is often not strong enough for the impaction forces applied. This often results in damage to the insertion tool, or metal shell or both.
A third category of prosthetic hip joint exists which is manufactured entirely from metal so that the prosthetic articulation comprises a metal on metal joint. These are nearly always implanted without cement, relying on a jam fit in the acetabulum. With this type of cup the inner hemisphere is not a convenient place to locate a mechanical feature for the insertion tool to grip on. First, it would reduce the surface area of the prosthetic articulation. Secondly, it could cause damage to the highly polished concave metal against which the ball of the patient""s femur or the ball head of a femoral prosthesis is to bear.
Therefore, the provision of means for attaching an insertion tool to a prosthetic implant so that the attachment is sufficiently robust to withstand the impaction and other forces to which it may be subject during insertion of the prosthesis and yet which does not compromise the structural strength or the articulating properties of the prosthesis itself remains a problem in the art.
Another disadvantage of conventional tools is that they must be manufactured in a range of different sizes to receive acetabular cups or sheaths of the different sizes referred to above.
The difficulty of gripping and positioning prosthetic implants applies not only to acetabular implants but more generally to implants such as the tibial and femoral components of a prosthetic knee.
U.S. Pat. No. 5,376,126 (Lin) discloses use of cords to assist in fastening a femoral implant to the upper end of a resected femur.
It is an object of the present invention to provide a prosthetic implant which does not suffer from one or more of the disadvantages of the prior art devices. It is further an object of the present invention to provide a surgical tool for use with such an implant.
Accordingly, the present invention provides a prosthetic implant comprising a main body portion, having a first surface for presentation to a receptive bone surface or to a surgically prepared bone cavity and a second surface for receipt of an articulating joint, and filamentary member attachment means adapted for attachment of a filamentary member to the implant.
The filamentary member can be a monofilamentary member, such as a Kevlar(trademark) monofilament, or a multifilament member such as a Kevlar(trademark) polyfilamentary thread or a metallic cable made, for example, from stainless steel. Such a cable may be, for example, from about 0.5 mm thick to about 2 mm thick. If desired, the cable can be coated with an inert material, such as polypropylene. Preferably the filamentary member is formed into a closed loop.
In one form of prosthetic implant according to the invention the filamentary member attachment means comprises a lug on the main body portion around which a filamentary member can be looped. Alternatively the filamentary member attachment means can comprise a bore in the main body portion through which a filamentary member can be threaded. In such a case it will normally be preferred to provide plurality of such bores, for example, three such bores.
The invention further provides such a prosthetic implant further comprising a cable attached to the main body portion of the implant by the filamentary member attachment means. Thus in a preferred embodiment of the invention the filamentary member attachment means comprises a plurality of bores in the main body portion and a filamentary member is threaded through each of the plurality of bores in turn, the free ends of the filamentary member being secured one to another so as to form a closed loop of filamentary member. The free ends of the filamentary member can be secured to one another by means of a sleeve having first and second ends, the sleeve snugly receiving a first looped portion of filamentary member located near a first end portion of the filamentary member and inserted from the first end of the sleeve so as to project as a first loop from the second end of the sleeve with the first end portion being passed through the first loop, and the sleeve further snugly receiving a second looped portion of filamentary member located near a second end portion of the filamentary member and inserted from the second end of the sleeve so as to project as a second loop from the first end of the sleeve with the second end portion being passed through the second loop, whereby upon tension being applied to the closed loop of filamentary member the first and second end portions of the filamentary member are firmly gripped by the first and second loops respectively.
The invention also provides an acetabular hip prosthesis for implantation in a surgically prepared socket in a hip of a patient comprising:
a generally cup-shaped body having:
an outer generally convex surface for contact with bone of a surgically prepared socket in a hip of a patient;
an inner generally concave surface;
a peripheral bridge portion whose surface extends between the outer generally convex surface and the inner generally concave surface; and
at least one bore which extends from a first opening in the surface of the bridge portion through an interior portion of the substantially cup-shaped body to a second opening in the surface of the bridge portion, the bore being adapted for receipt of a filamentary member therethrough for holding the prosthesis on the end of an insertion tool to facilitate insertion of the prosthesis into the prepared socket.
In such an acetabular hip prosthesis there is preferably provided a plurality of bores each of which extends from a first opening in the surface of the bridge portion through an interior portion of the substantially cup-shaped body to a second opening in the surface of the bridge portion, the bore being adapted for receipt of a filamentary member therethrough for holding the prosthesis on the end of an insertion tool to facilitate insertion of the prosthesis into the prepared socket.
Preferably the outer generally convex surface of the cup-shaped body is provided with a coating of hydroxyapatite and also is texturised to facilitate ingrowth of bone after implantation into a surgically prepared hip socket of a patient.
In another aspect of the invention there is provided a protected prosthetic implant comprising a main body portion, having a first surface for presentation to a receptive bone surface and a second surface for receipt of an articulating joint, filamentary member attachment means adapted for attachment of a filamentary member to the implant, and a protective cap for covering at least part of the second surface of the main body portion of the implant. The protective cap can be attached to the main body portion of the implant by means of a cable. In this case the cable can be tensioned so that the protective cap is tightly attached to the main body portion of the implant.
The protective cap is preferably made of a rigid material. It can be provided with a number of holes, through which the filamentary member is threaded for attachment of the protective cap to the prosthetic implant.
It will often be preferred for the protective cap to be a disposable protective cap. Alternatively it can be reusable after appropriate sterilisation.
The invention further provides a protected acetabular hip prosthesis for implantation in a surgically prepared socket in a hip of a patient comprising:
(i) a generally cup-shaped metal body having:
an outer generally convex surface for contact with bone of a surgically prepared socket in a hip of a patient;
an inner substantially part spherical cavity in the metal body, the cavity having a generally concave polished surface for receipt of a ball head on a femoral prosthesis and a periphery surrounding the cavity and defining a mouth;
a peripheral bridge portion whose surface extends between the periphery of the cavity and the outer generally convex surface; and
at least one bore which extends from a first opening in the surface of the peripheral bridge portion through an interior portion of the substantially part spherical body to a second opening in the surface of the bridge portion, the at least one bore being adapted for receipt of a filamentary member therethrough for holding the prosthesis on the end of an insertion tool to facilitate insertion of the prosthesis into the surgically prepared socket;
(ii) a cover member adapted to bridge the cavity, the cover having apertures therethrough which correspond to the first and second openings in the metal body and are adapted for passage of the filamentary member; and
(iii) a filamentary member threaded through the at least one hole in the metal body and through the apertures in the cover member, the free ends of the filamentary member being secured one to another to form a closed loop of filamentary member which secures the cover to the metal body.
Yet again the invention provides a protected acetabular hip prosthesis for implantation in a surgically prepared socket in a hip of a patient comprising:
(i) a generally cup-shaped metal body having:
an outer generally convex surface for contact with bone of a surgically prepared socket in a hip of a patient;
an inner substantially part spherical cavity in the metal body, the cavity having a generally concave polished surface for receipt of a ball head on a femoral prosthesis and a periphery surrounding the cavity and defining a mouth;
a peripheral bridge portion whose surface extends between the periphery of the cavity and the outer generally convex surface; and
a plurality of bores each of which extends from a first opening in the surface of the peripheral bridge portion through an interior portion of the substantially part spherical body to a second opening in the surface of the bridge portion, the bores being adapted for receipt of a filamentary member therethrough for holding the prosthesis on the end of an insertion tool to facilitate insertion of the prosthesis into the surgically prepared socket;
(ii) a cover member adapted to bridge the cavity, the cover having apertures therethrough which correspond to the first and second openings in the metal body and are adapted for passage of the filamentary member ; and
(iii) a filamentary member threaded through each of the plurality of holes in the metal body and through the apertures in the cover member, the free ends of the filamentary member being secured one to another to form a closed loop of filamentary member which secures the cover to the metal body.
In addition, the invention provides a protected acetabular hip prosthesis for implantation in a surgically prepared socket in a hip of a patient comprising:
(i) a generally cup-shaped metal body having:
an outer generally convex surface for contact with bone of a surgically prepared socket in a hip of a patient;
a cavity in the metal body for receipt of a liner of plastics material, the cavity having a periphery surrounding the cavity and defining a mouth;
a peripheral bridge portion whose surface extends between the periphery of the cavity and the outer generally convex surface; and
a plurality of bores each of which extends from a first opening in the surface of the peripheral bridge portion through an interior portion of the substantially part spherical body to a second opening in the surface of the bridge portion, the bores being adapted for receipt of a filamentary member therethrough for holding the prosthesis on the end of an insertion tool to facilitate insertion of the prosthesis into the surgically prepared socket;
(ii) a liner of plastics material secured in the cavity of the cup shaped metal body, the liner having an outer surface adapted to conform to the inner surface of the cavity in the cup-shaped metal body and a substantially part spherical inner surface for receipt of a ball head on a femoral hip prosthesis;
(iii) a cover member having a first face adapted to bridge the cavity, the cover member having apertures therethrough which correspond to the first and second openings in the metal body and are adapted for passage of the filamentary member ; and
(iv) a filamentary member threaded through each of the plurality of holes in the metal body and through the apertures in the cover member, the free ends of the filamentary member being secured one to another to form a closed loop of filamentary member which secures the cover to the metal body.
Preferably the cavity in the cup-shaped metal body is provided with an inwardly projecting lip surrounding the mouth of the cavity and the liner is provided with a peripheral ledge which is adapted to snap fit under the inwardly projecting lip of the cup-shaped metal body. It will also often be preferred that the cavity in the cup-shaped metal body is provided with a circumferential internal ridge below and adjacent the inwardly projecting lip and wherein the liner is provided with a corresponding circumferential groove on its outer surface which is adapted to receive the circumferential ridge. It will further often be desirable for the liner to be is made from high density polyethylene. In one particularly preferred form of the invention the cover member is provided on a second face opposite its first face with an axial blind bore for location of a corresponding axial locating peg on an insertion tool. In addition the cover member can be provided on its second face with an auxiliary bore whose axis is parallel to and offset from the axis of the axial blind bore, the auxiliary bore being adapted to receive a corresponding offset peg on an insertion tool to prevent relative rotation of the acetabular hip prosthesis and cover member about the axis of the axial locating peg of the insertion tool.
In another aspect of the invention there is provided a surgical tool for gripping a protected acetabular hip prosthesis for implantation in a surgically prepared socket in a hip of a patient, the protected acetabular hip prosthesis comprising a generally cup-shaped metal body which has an outer generally convex surface and a cavity defining a mouth, a protective cap over the mouth of the cavity, and a closed loop of filamentary member secured to the acetabular hip prothesis, the tool comprising an elongated body having a first end for engagement with the protective cap and adjustable filamentary member engagement means for engagement with and tightening of the closed loop of filamentary member so as to locate the protective cap against the first end of the tool and to draw the acetubular hip prosthesis towards the first end surface thereby to hold the prosthetic implant securely on the first end of the tool during surgical implantation of the acetabular hip prothesis, the tool and protective cap being removable after such surgical implantation by loosening the tension in the closed loop of filamentary member and then severing the closed loop of filamentary member to allow it to be disengaged from the implanted acetabular hip prosthesis.
Also provided in accordance with the invention is a surgical tool for gripping the prosthetic implant of the invention, comprising an elongate body having a first end surface for bearing on the implant and means on the tool adapted for attachment thereto of a cable from the implant.
The attachment of the tool to the prosthetic implant is achieved by means of a filamentary member, such as a cable. The attachment may be a direct attachment, in which case a cable is passed between the implant and the tool and secured to each by the respective attachment means. The attachment may be an indirect attachment, by which is meant that the cable may be used to attach a protective cover to the prosthetic implant and the tool may then be attached to the protective cover. Embodiments of the invention which make use of this indirect attachment will be described in more detail below.
The filamentary member attachment means on the prosthetic implant may comprise a lug on the main body portion of the implant around which a cable or other filamentary member can be looped. Alternatively, or also, the filamentary member attachment means may comprise a bore in the main body portion of the implant through which a cable can be threaded.
The adjustable filamentary member attachment means on the tool may comprise a mooring peg on the tool. The mooring peg may be mounted on a carriage which is movable axially within the body of the tool to tension the cable. Alternatively the adjustable filamentary member attachment means on the tool may comprise a spring loaded arm on the tool. The arm may be mounted on a carriage which is movable axially within the body of the tool to tension the cable or other filamentary member.
The cable or other filamentary member may be an endless cable which may be looped around or threaded through the filamentary member attachment means. Alternatively, a length of cable may be used and secured to each filamentary member attachment means by any convenient means, such as a tie, clip, or knot. Any convenient number of cables or other filamentary members may be used and any convenient number of attachment means on the prosthetic implant and on the surgical tool may be employed. For example, in one preferred embodiment of the invention, the prosthetic implant is an acetabular cup comprising three means. Each filamentary member attachment means is preferably spaced evenly from an adjacent filamentary member attachment means around the rim of the cup. The surgical tool may also comprise three adjustable filamentary member attachment means. Each of these adjustable filamentary member attachment means is preferably spaced evenly around the circumference of the tool from an adjacent filamentary member attachment means. The filamentary member is preferably an endless stainless steel cable which passes from a first filamentary member attachment means on the cup to a first corresponding adjustable filamentary member attachment means on the tool and then on to successive respective second and third attachment means on the implant and on the tool, returning in an endless loop to the first filamentary member attachment means on the cup.
The surgical tool and prosthetic implant of the invention have a number of significant advantages over the prior art. The use of a cable or other filamentary member to provide, directly or indirectly, means for securing the implant to the insertion tool means that any compromise in the structural and functional integrity of the implant as a result of the attachment is minimised. The diameter of the cable may be quite small, for example from about 0.5 mm to about 2 mm, and the means for attachment of the cable to the implant may be correspondingly small. For example, a bore of from about 0.5 mm to about 2 mm in the rim of a prosthetic acetabulum of cobalt chrome will not compromise the strength of the implant to any serious degree. Similarly, the provision of lugs having sufficient protrusion to allow a cable of from about 0.5 mm to about 2 mm diameter to be looped therearound on the outer surface of the acetabulum, adjacent the rim thereof, will not interfere to any serious degree with the positioning of the implant in the bone cavity.
The use of a cable or other filamentary member to secure the implant to the tool also has the advantage that the visibility of the attachment area by the surgeon is maintained at a significantly high degree. It is often important for the surgeon to be able to see clearly the position of the implant with respect to the bone surface or cavity.
The surgical tool of the invention may further be provided with means for tensioning the cable or other filamentary member after attachment of the cable to the tool to bring the first end surface of the tool to bear upon the implant. For example, the first end surface of the tool may comprise one or more flanges for bearing on the rim of an acetabular cup. The adjustable filamentary member attachment means on the tool may comprise one or more mooring pegs on the tool, the or each mooring peg being mounted on a carriage which is movable axially within the body of the tool to tension the cable. Alternatively the adjustable filamentary member attachment means on the tool may comprise a spring loaded arm on the tool, the or each arm being mounted on said carriage. Preferably, the carriage is carried on a screw-threaded member mounted axially within the body.
When used, the protective cover may be a disposable protective cover, or it may be reusable after appropriate sterilisation. The protective cover is preferably of a rigid material, for example polyethylene. Preferably, the protective cover is provided with a number of holes, through which the cable is threaded for attachment to the main body portion of the prosthetic implant. The main body portion of the prosthetic implant may comprise one or more lugs, around which the cable may be looped for attachment of the main body portion to the protective cover by means of the cable. Alternatively, or also, the main body portion of the prosthetic implant may be provided with one or more bores through which the cable may be threaded for attachment of the main body portion to the protective cover by means of the cable.
The means for attachment of the tool to the protective cover may comprise a shaped plug on one end of the tool, the plug being receivable within a corresponding socket provided on the protective cover. Preferably, a biased locating pin is provided on the tool, the pin being locatable within a corresponding opening provided on the protective cover, the biasing urging the pin into the opening to prevent rotation between the insertion tool and the implant so that rotational forces can be applied to the implant by means of the tool when the implant is positioned or impacted.
Alternatively, or also, the means for attachment of the tool to the protective cover may comprise means on the tool for attachment of the cable thereto. In this case, there may further be provided means for tensioning the cable after attachment of the cable to the tool to bring the first end surface of the tool to bear upon the protective cover. The means on the tool for attachment of the cable may comprise one or more mooring pegs on the tool, the or each mooring peg being mounted on a carriage which is movable axially within the body of the tool to tension the cable. Alternatively the means for attachment of the cable may comprise one or more spring loaded arms being mounted on said carriage. Preferably, the carriage is carried on a screw-threaded member mounted axially within the body.
When a protective cover is used in the implant of the invention, there is no necessity to manufacture surgical tools of different sizes to correspond to different sizes of acetabular cup or sheath. It is sufficient that the protective cover comprise a receiving area for the surgical tool. When a tensioned cable is used to grip the prosthetic implant the attachment provided is robust in lateral and axial directions, whilst allowing the surgeon to retain good visibility of the implant during the surgical procedure.
When a tensioned cable is used to effect direct attachment between the implant and the tool, the surgeon is allowed not only a good degree of rotational and axial control over the implant whilst inserting the implant, but also the surgeon is able to extract the implant if he is not satisfied with its orientation after initial insertion.
When any of the embodiments of the invention are applied to the implantation of a prosthetic acetabular cup comprising a polyethylene unit and a metal shell, it is not necessary for the polyethylene liner unit to be snapped or screwed into the metal shell after it has been seated in the acetabulum. A result of this is that the polyethylene liner unit may be factory fitted reducing the risk of damage to the unit during fitting.